This map is one of a series of four 1:25,000-scale quadrangle maps (Anchorage C-7 NW Quadrangle) intended to provide information on the geology and construction materials along the southern margin of the Talkeetna Mountains between Little Susitna River and Nancy Lake, Alaska. Additionally, the geologic map portrays faults, if present, as well as other lineaments that represent either faults or erosional features.

Supplemental_Information:

The layers listed below are present as ArcGIS shape files. Attribute information for the following layers (entities) is included in this metadata file under the "Entity_and_Attribute_Information" section. Each layer is listed and described in detail under its own heading starting "Entity_Type_Label." Basic unit information is also included in the geologic unit code set file "RI1994-24-27_codeset.pdf." Layers include:

Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.000032
Ordinates (y-coordinates) are specified to the nearest 0.000032
Planar coordinates are specified in meters

The horizontal datum used is D_Clarke_1866.
The ellipsoid used is Clarke 1866.
The semi-major axis of the ellipsoid used is 6378206.4.
The flattening of the ellipsoid used is 1/294.978698.

Object type is vector, there are 276 rows associated with this entity, and the entity values refer to the unit name abbreviations for each specific polygon represented on the map.
(Source: Alaska Division of Geological & Geophysical Surveys)

UNIT

A unique three to four letter abbreviation given to each map unit represented on the map. Any unit ending with a "?" indicates uncertainty.
(Source: Alaska Division of Geological and Geophysical Surveys)

Represents the X-coordinates in UTM for each strike and dip location.
(Source: Alaska Division of Geological and Geophysical Surveys)

Range of values

Minimum:

360979.4

Maximum:

371214.3

Units:

meters

Y-COORD

Represents the Y-coordinates in UTM for each strike and dip location.
(Source: Alaska Division of Geological and Geophysical Surveys)

Range of values

Minimum:

6834746

Maximum:

6848709

Units:

meters

ancc7nwflt2_arc.shp

Object type is vector, there are 44 rows associated with this entity, and the entity values refer to fault location traces and types.
(Source: Alaska Division of Geological & Geophysical Surveys)

CODE

Types of faults found in the map area.
(Source: Alaska Division of Geological and Geophysical Surveys)

Value

Definition

1

Contact

2

Contact, approximate

3

Scarp, barb on lower side

5

Trough, may be ice-marginal channel at lower elevations

6

Photolineament with no topographic expression evident in aerial photographs. Generally visible as a color or density contrast in vegetation.

c7nwdip_point.shp

Object type is point, there are 38 rows associated with this entity, and the entity values refer to symbols for strike and dip information.
(Source: Alaska Division of Geological & Geophysical Surveys)

DIP

Represents the dip angles used to produce the dip directions.
(Source: Alaska Division of Geological and Geophysical Surveys)

Range of values

Minimum:

0

Maximum:

90

CODE

Represents the symbols used to describe the strike and dips of beds and foliation.
(Source: Alaska Division of Geological and Geophysical Surveys)

Value

Definition

1

Strike and dip of foliation. Also shown as SYMBOL=105.

2

Dip is equal to zero. Also shown as SYMBOL=112.

3

Strike and dip of beds. Also shown as SYMBOL=101.

SYMBOL

Represents the symbols used to describe the strike and dips of beds and foliation.
(Source: Alaska Division of Geological and Geophysical Surveys)

Value

Definition

101

Strike and dip of beds. Also shown as CODE=3.

105

Strike and dip of foliation. Also shown as CODE=1.

112

Dip is equal to zero. Also shown as CODE=2.

X-COORD

Represents the X-coordinates in UTM for each strike and dip location.
(Source: Alaska Division of Geological and Geophysical Surveys)

Range of values

Minimum:

364018.304525507

Maximum:

371181.671787229

Units:

meters

Y-COORD

Represents the Y-coordinates in UTM for each strike and dip location.
(Source: Alaska Division of Geological and Geophysical Surveys)

Range of values

Minimum:

6838020.78915279

Maximum:

6848152.14758965

Units:

meters

ancc7nwsack2_arc.shp

Object type is vector, there are 2 rows associated with this entity, and the entity values refer to polygons showing sackung failure in bedrock.
(Source: Alaska Division of Geological & Geophysical Surveys)

CODE

Represents the areas of the sackung failures in bedrock.
(Source: Alaska Division of Geological and Geophysical Surveys)

Object type is vector, there are 3 rows associated with this entity, and the entity values refer to fault location traces and types. There are no attributes associated with this entity.
(Source: Alaska Division of Geological & Geophysical Surveys)

Preparation of these maps was supported in part by the U.S. Geological Survey through the STATEMAP component of the National Cooperative Geologic Mapping Program.
Additional Acknowledgments: Field assistance provided by Cheri Daniels, Kristin Kline, and Gina Cruse. Reviewed by Jim Clough and Jeff Kline.

You may view our web site at <http://www.dggs.alaska.gov> for the latest information on available data. Please e-mail your questions and data requests when possible since our web site and e-mail address will remain current even if our phone number and mailing address change.

This series of maps supplements an earlier series of similar maps for the adjacent area to the south between Palmer and Big Lake. A separate geologic-materials map was developed to show the probable distribution of materials with certain ranges of grain sizes, and their relative abundance, because the area is rich in geologic materials that may be useful for construction. It is an important source of construction aggregates for the region, because of extensive glaciofluvial deposits in the area. Additionally, the Castle Mountain fault, which is known to be active, traverses the area of the current series of maps. Although the fault is easily distinguishable in areas immediately to the east and west of the area mapped in this series, it is largely obscured here by surficial deposits and vegetation. We present on these maps the best known surface evidence for faults and possibly fault-related lineaments.

Geologic map preparation - Data collection for this series of maps took place over approximately a 15-year period from 1980 to 1994. The geologic map was developed by first interpreting landforms and photolineaments on color and false-color infrared photographs. These deposits and features were then verified, described, and sampled during field inspections. Additionally, information on bedrock geology was compiled from the literature and verified and mapped in the field. Finally, the bedrock and surficial geology were combined into a single draft map and digitized. The geologic-materials map was derived digitally from the geologic map on the basis of field observations that indicate that each geologic unit has a definite composition or range of composition. Therefore, the delineation of materials units was interpreted from the geologic map by using a simple conversion matrix to combine and translate geologic units into materials units. Much of the initial landform interpretation and mapping of geologic contacts and lineaments resulted from analysis of color and false-color infrared vertical aerial photographs. Color aerial photographs used in this interpretation were taken in 1973, 1981, 1982, and 1986 at scales of 1:12,000, 1:18,000, and 1:24,000. False-color infrared images were collected by NASA in 1984 and 1993 at a scale of approximately 1:60,000. Bedrock-geologic data were compiled from the following sources: Clardy (1984), Csejtey and others (1978), Csejtey and others (1979), Csejtey and Smith (1975), Madden and others (1987), Magoon and others (1976), Ray (1954), Silberman and others (1978), and Winkler (1992). Field work was conducted in 1980, 1981, 1988, 1993, and 1994 to verify photointerpretation, map bedrock-unit contacts, and examine the deposits to accurately describe their content. Finally, the draft geologic map units were digitized using geographic information system (GIS) software. The resulting polygons were assigned appropriate colors, labeled, and layered with a digital image of the corresponding U.S. Geological Survey topographic quadrangle map to produce the published geologic map. The USGS topographic base map was produced in 1979 and revised in 1993.

Geologic point, line, and polygon data were determined in the field using 1:63,360-scale topographic maps and 1:50,000 (nominal) scale, color-infrared aerial photographs. The surficial-geologic information was transferred from acetate air-photo overlays to a paper 1:63,360-scale USGS topographic base using a zoom transfer scope. The surficial-geologic information was then digitized into Arc/Info GIS (ArcEdit module) using a large-format digitizing table with RMS registration errors constrained to be no larger than 0.003 inches (input coverage units) for each digitizing session. Geologic data included in the compilation are the field maps and notes from this project as well as data from other sources as noted in the "Sources Cited" section.

This report, map, and/or data set are available directly from the State of Alaska, Department of Natural Resources, Division of Geological & Geophysical Surveys (see contact information below).

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